The overall objective of this project is to determine the mechanisms by which electronic energy can be degraded in large organic molecules and molecular complexes. These studies involve photoreactivity of metalloporphyrin complexes, especially ruthenium (II), zinc, palladium, iron, magnesium and platinum; olefins; dienes and polyenes in solution and in organized monolayer assemblies. For the porphyrins key photoreactions under investigation include CO photoejection, reversible oxygenation and formation of metal-metal bonded dimers. These reactions are being investigated in solution, in the solid state, and in organized monolayer assemblies. In addition the formation of triplet exciplexes from porphyrins and aromatic compounds in solution is under investigation. The spectroscopic behavior of these species in monolayer films is also being studied. Both the effect of the semi-rigid environment provided by the monolayer assembly on molecular reactivity and the effect of component reactions on macroscopic properties of the membrane-like assemblies are being determined for assemblies containing olefins, dienes and polyenes.